Bhitush Luthra (Email – bhitush@cseindia.org)

Centre for Science and Environment, New Delhi

Faecal Sludge Treatment

Options

Criteria: Selection of Technology

• Design a system based on final end-use or disposal option of treatment

products

• Designing a system for the actual quantity and characteristics of faecal

sludge.

• Design system based on the collection and transport approaches

• Develop a system by understanding treatment mechanisms

• Develop system based on the resource required – land, cost, skills

• Develop system based on Operation and maintenance requirements

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Source: 1. Fecal sludge management systems approach for implementation and Operation, IWA Publications, 2014

2. Sandec Training Tool- Fecal sludge management

Treatment – Objectives

Selection of treatment options based on achievement

of following objectives

Priority

Highest

Pathogen Removal

Organic Load Reduction

Reuse Lowest

Goals for Sludge treatment

• Solid-liquid separation • Stabilisation • Dewatering/drying • Pathogen reduction • Beneficial enduse

Categorisation of Sludge Treatment Options

Solid-liquid

separation

SEDIMENTATION / THICKENING PONDS

DIGESTOR

Stabilisation

IMHOFF TANK

ABR

Dewatering /

drying

UNPLANTED DRYING BEDS

MECHANICAL DEWATERING (E.G. FILTER PRESS, CENTRIFUGE)

CO-COMPOSTING MECHANICAL / HEAT DRYING

Pathogen reduction

PLANTED DRYING BEDS

STORAGE AND FURTHER DRYING

(E.G. PELLETISER)

VERMICOMPOSTING / BLACK SOLDRIER FLIES

CO-COMBUSTION

Source : EAWAG

Possible Treatment Options

Primary Treatment

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Screening

• The screen and Grit chamber is a

basin to trap large solids (rags, paper,

plastics, and metals)using different size

screens and for settling of grits (sand,

gravel, cinder)

• The screens are provided with parallel

bars vertically or horizontally with a

opening size of 2 to 5cm

• The solids collected in this chamber

removed regularly and disposed safely

Settling Tanks and Sedimentation Ponds

• Settling tanks provide a liquid

retention time of a few hours (to

ensure settling of Settleable

solids)

• Sedimentation ponds provide a

liquid retention of few days or

several weeks

• designed on

• Desired depth and

• Quantity of accumulating

solids

• The accumulating solids have

to be removed and treated

further

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Sedimentation / Thickening Ponds

Sedimentation / thickening ponds Dakar, Senegal

Sludge Drying Beds

• It is a shallow filter tank filled with graded

gravel mainly used for dewatering of

stabilized sludge

• Graded filter media of different diameter

used for the depth of 50-60cm depth with

the top layer as sand

• Approximately 50-80% of the liquid drains

of as filtrate and 20-50% due to

evaporation

• The depth of sludge applied per loading is

not more than 30cm

• Sludge drying period range of 10-20 days

depending on the temperature

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Unplanted Drying Beds

Unplanted drying beds

Dakar, Senegal

Planted Sludge Drying Beds

• FS is loaded with layers of sludge that

are subsequently dewatered and

stabilized through multiple physical and

biological mechanisms

• The beds consist of gravel/sand/soil

filter planted with plants such as reeds,

cattails, bulrushes

• Liquid fraction

through

flows vertically

media and is

bottom and treated

downwards

collected at

separately

• Sludge retention time is 2-3 years

depending on sludge loading rate TS

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Planted Sludge Drying Beds

Planning & Design for Sanitation

Co-treatment with Wastewater

Co – Composting with Municipal Solid waste

Stabilization/Treatment

Anaerobic Digestion: Biogas digester

LaDePa pelletizer

Mechanical Treatment Options

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Co-treatment with Wastewater

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Septage addition at the nearest sewer

manhole, upstream of STP

Septage addition at STP

Septage addition to Sludge Digesters / Sludge Drying Beds

Co – Composting with Municipal solid waste

• Co-composting is a mixture of organic

solid waste and faecal sludge with pre-

defined moisture content (40-60%) at

specified condition

• Human waste is rich with Nitrogen and

moisture content; solid waste has high

organic carbon content

• Co – composting of Faecal Sludge and

organic solid waste range from 1: 2 –

1:10 depending on the Faecal Sludge

characteristics and its water content

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Co-Composting

Anaerobic Digestion

e

• This process ensure effective sludge

digestion and stabilization

• During digestion:

1. Organic matter is converted to biogas

2. The stabilized sludge (digestate)

utilized as soil conditioner

• The SRT is maintained for 10-15 days

• Removal of accumulated solids from th

digester remain a challenge

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Mechanical Treatment Options

• The technologies used to treat wastewater sludges are also

applicable for Faecal Sludge namely:

1. Belt Filter Press

2. Frame Filter Press

3. Screw Press

4. Centrifuge

• Advantages of mechanical treatment options include

compactness and speed of the process

• Limitations of mechanical treatment options include high

investment costs, O&M and electricity requirements

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Mechanical Treatment Options

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Lime Treatment

• Objective of lime addition is to achieve

reduction of pathogens, odor and

degradable organic matter

• The level of digestion depends on the

degree of the initial stabilisation of FS, the

temperature, and on the retention time

inside the tank

• As per the experience in order to achieve

the desired results, it is proposed to 5 kg of

lime per cum of sludge

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Integrated faecal sludge

Treatment Systems

Faecal Sludge/Septage

Screen Chamber

Sand and grit

removal

Settling Tank

Separation - free

water

Solids

Anaerobic based approach for Faecal sludge treatment

Anaerobic digester

Stabilization

Liquid-solid

separation

Disposal

Liquid Treatment Effluent is discharged

into agricultural

fields, drain or water

body

DEWATS

Disposal Liquid

Unplanted drying bed

Dewatering

Solids

Co-composting

Disinfection

Enriching fertilizer value

1. Regular operator is required. O&M is simple

2. Capital cost is high and recurrent cost is minimal

3. Large area requirement (UG+OG)

4. Suitable for large quantity (20cum)

5.

6.

Good treatment efficiency

Regular feeding is not a issue End product is

compost. Can

be used as

soil

conditioner

Cost- INR: 25,000-40,000/cum

Faecal Sludge/Septage

Screen Chamber

Sand and grit removal

Planted Drying beds

Stabilization

Dewatering

Disinfection

Aerobic based approach for Faecal sludge treatment

Co-composting

Solids

End product is compost. Can be used as soil conditioner

Disposal

Liquid Treatment Effluent is

discharged into agricultural fields,

drain or water body

DEWATS Disposal

Disinfection

1. Commonly practiced technique due to simplicity

2. Moderate capital cost, Low recurring cost

3. Large area requirement

4. Good treatment efficiency

5. Location of the treatment system may be an issue – odor, flies

6. Operation and mainatainace may be an issue – acceptance 7. Regular feeding may be an issue

Cost- INR: 40,000-60,000/cum

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Thank You!

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